Streamable HTTP: JSON-response-mode stream mappings never complete their lifecycle

[felixweinberger]

With enableJsonResponse: true on a stateful transport, send() resolves the pending Response via resolveJson but never runs the mapping's cleanup, so every completed POST leaks one _streamMapping entry until close(). Conversely, cleanup only deletes the entry without settling the promise, so close() during an in-flight JSON-mode POST leaves the HTTP request hanging.

Pre-existing on both main and v1.x. Split out from the review discussion on #2547.

[KXHXK]

I'd like to work on this. I confirmed there is no linked or open implementation PR.\n\nOn the current main branch, the successful JSON-response path already calls stream.cleanup() after resolving the response, so I would focus the v2 fix and regression coverage on settling an in-flight JSON response during transport shutdown, then verify the remaining lifecycle behavior on �1.x separately.\n\nPlease assign this to me if that scope is available.

[axits-lab]

@felixweinberger Happy to take this one too, after the #2562 items.

Reading it as two halves of one lifecycle bug: send() resolves via resolveJson without running the mapping's cleanup (so a completed POST leaks its _streamMapping entry until close()), while cleanup deletes the entry without settling the promise (so close() during an in-flight JSON-mode POST leaves the request hanging). Fix is to make both paths run the full lifecycle — settle and delete — rather than one each.

Since you note it's pre-existing on both main and v1.x, should the v1.x fix be a separate PR against that branch, or do you prefer main first and a backport after?

[axits-lab]

Up as #2584 (draft — one-open-PR cap, #2582 holds it).

One note: only the second half reproduced. The cleanup-never-settles hang is real and fixed there. The _streamMapping leak doesn't reproduce on main — send() has called stream.cleanup() on both branches since #2286 (merged 2026-06-26), and measuring directly gives _streamMapping.size === 0 after a completed JSON-mode POST. I left that half alone rather than write a change that does nothing; happy to look again if you're seeing it on a path I didn't hit.